High tension circuit breakers fitted with varistors exist, particularly for switching shunt reactances in electricity networks. The purpose of having varistors (also known as non-linear resistors, or as variable resistors, or as voltage-dependent resistors) is to reduce surge.
The lower the operating threshold of a varistor, the more effective the protection it provides against surge. To obtain a varistor operating threshold which is low, only a small number of varistor components should be connected in series, with the drawback that the energy absorbed by each varistor component is then high.
The limiting surge value for which varistors can provide protection is presently about 1.6 pu (where 1 pu=Un .times..sqroot.2/.sqroot.3 peak value, with Un being the nominal phase voltage).
In order to limit surge below 1.6 pu, proposals have been made to put a switch in series with the varistor for the purpose of separating the varistor from the network after the circuit breaker has been disengaged.
An object of the present invention is to provide a circuit breaker based on this principle which is simple and cheap to manufacture.
The invention is equally applicable to conventional type and to metal-clad type circuit breakers in which the varistor for each of the poles of the circuit breaker is placed in a case that is distinct from the case containing the interrupting chamber, as to circuit breakers in which the varistor is placed in the same case as the interrupting chamber.
The invention is applicable to circuit breakers having a plurality of interrupting chambers connected in series with each phase, and it applies in particular to circuit breakers having two interrupting chambers per phase in a T or a V configuration.